For many years agriculturists have known of and benefited from the advantages of mulches, such as straw, salt hay, and other organic ground covers, in providing a measure of control over weed growth, root zone temperature, and soil moisture, particularly with field crops of fruits and vegetables. More recently, continuous webs of impervious films of plastics, such as polyethylene, both transparent and opaque, have found similar application and even greater adaptability to the large acreage operations of commercial agriculture.
Initially, the strength and waterproof nature of these film materials were considered assets in that they allowed mechanized application over the lands under cultivation and provided soil moisture containment as well as prevention of leaching of soil nutrients by rainwater throughout the growing season. These properties soon became liabilities, however, since they contributed to a longevity in the plastic materials which by far exceeded the normal term of their utility as mulch. The lack of degradability in these materials has resulted in a persistency which threatens the future utility of untold numbers of acres of otherwise valuable farmlands.
In order to avoid further contamination of these lands by plastic film debris, it has become imperative that these mulch materials be retrieved at the end of the growing season. In addition to the significant expense of cleanup operations, the lack of manpower late in the season has made the task nearly impossible for farmers of moderate means. A further deterrent to the use of plastic films where recovery is not entirely impractical has been the increasingly stringent limitations by environmental regulation upon the disposal of the resulting persistent plastic waste materials.
The need has long been recognized for a continuous web mulch product which would provide the handling capabilities and agricultural benefits of plastic film, yet would be degradable after a reasonably long growing season. Numerous attempts have been made to impart degradability to plastic films or to improve the physical properties of paper webs without reducing the inherent degradability of such materials; however, there previously has resulted no successful product of this type.
Such attempts have taken the form, for example, of polyolefin film with incorporated degrading agents (U.S. Pat. No. 3,795,654) or photodegradable polymer film (U.S. Pat. No. 3,590,527), and of creped kraft paper saturated with oil (U.S. Pat. No. 2,685,150) or fungicides (U S. Pat. No. 3,493,464), or laminated to plastic film (U.S. Pat. No. 3,810,328). The shortcomings of these materials have ranged from the unpleasant mess of the oil-soaked paper to the fact that the impervious plastic films and film laminates do not actually degrade, but merely break apart to yield smaller, yet substantially sized pieces which nonetheless infect the land. On the contrary, the material of the present invention provides the benefits of weed control and soil condition maintenance during the growing season, but thereafter, being truly biodegradable, disintegrates and disperses throughout the soil.